The providers of popular, large digital files, such as software, music or video files, must keep pace with the ever increasing bandwidth demands for delivering such files. As the popularity of a file increases, a larger number of users are requesting the file and more bandwidth is required to deliver the file. With conventional Hypertext Transfer Protocol (HTTP) file delivery techniques, for example, the bandwidth requirements increase linearly with the number of requesting users, and quickly become prohibitively expensive.
A number of techniques have been proposed or suggested for reducing the bandwidth demands of file delivery on the server, using peer-to-peer content sharing. In a peer-to-peer content sharing model, often referred to as “cooperative distribution,” one or more users that have downloaded one or more files from the server can share the file(s) with other users. A cooperative distribution model allows a server to deliver large files in a reliable manner that scales with the number of requesting users. Among other benefits, cooperative distribution models exploit the underutilized upstream bandwidth of existing users.
The BitTorrent™ file distribution system, described, for example, in http://www.bittorrent.com/documentation.html, or Bram Cohen, “Incentives Build Robustness in BitTorrent,” http://www.bittorrent.com/bittorrentecon.pdf (May 22, 2003) is an example of a cooperative distribution technique. When multiple users are downloading the same file at the same time using the BitTorrent file distribution system, the various users upload pieces of the file to each other. In other words, a BitTorrent user trades pieces of a file that the user has with other required pieces that other users have until the complete file is obtained. In this manner, the cost of uploading a file is redistributed to the users of the file and the cost of hosting a popular file is more affordable. In addition, U.S. patent application Ser. No. 11/096,193, filed Mar. 31, 2005, entitled “Method and Apparatus for Offline Cooperative File Distribution Using Cache Nodes,” discloses a cooperative file distribution system that uses one or more storage proxies to store the files that are being transferred among users.
While such cooperative file distribution systems provide an effective mechanism for distributing large files in a cost effective manner, they suffer from a number of limitations, which if overcome, could further improve the utility and efficiency of cooperative file distribution. In particular, it is difficult to guarantee a desired quality of service, such as a desired data delivery rate. A need therefore exists for improved cooperative file distribution systems that can satisfy a target data delivery rate. Yet another need exists for cooperative file distribution systems that supplement the peer-to-peer content sharing with more reliable data sources, such as web servers.